Four grades of sinter hardening materials have been compared, using industrial equipment. Three powder types were completely prealloyed; the last one was a hybrid, combining prealloying and diffusion bonding. Different amounts of Cu have been added by mixing. The lubricated mixes, containing 0 . 6% graphite, have been compacted at different pressures, to form gears at green densities >7 . 0 g cm 23 ; the compacts have been sintered at 1120uC, under endogas from methane and fast cooled (at least 7 K s 21 within the range 850-400uC). The final step has been stress relieving, at 180uC, for 1 h. Material properties have been investigated, focusing on porosity, pore shape, hardness, microhardness, microstructure, local chemical composition and mechanical properties. For comparison, other gears, compacted in the same tool and at the same density level, but manufactured according to a more conventional cycle, i.e. starting from less alloyed powders and adding carbonitriding, quenching and stress relieving, have been used. The analysis of the different experimental results enabled the authors to find out and outline some criteria suitable for selecting sinter hardening materials and for choosing more reliable manufacturing conditions to fulfill specific application requirements.

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The hardenability of some PM steels designed for heat treatment has been evaluated on sintered steel specimens by applying the procedure standardised with the Jominy end quench test. The samples have been produced using two types of commercial powders, frequently selected for exacting applications. Manufacturing process includes admixing with graphite and lubricant, compaction at about 7 . 0 g cm 23 density and sintering at 1393 K for 30 min in industrial equipment. In order to investigate the thermal behaviour of the tested steels, during the cooling after austenitising, the temperatures inside the Jominy samples at different positions have been recorded. Hardness values and cooling rates have been correlated to an in depth microstructural analysis and microhardness profiles, finding a good agreement. The results can be utilised for a more reliable applications.

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